Change admin user name

Hi guys,

I wanted to change an admin user name in 14.0.4. Therefore I found a post of a Version 9 where you should add a new user, grant access rights an delete the old one. I got no data in on of the admin accounts
The issue is right now is, that I cannot delete the old admin account, thought I already deleted the group “admin” of that account. The selection on the right side for deleting or deactivating is completely missing for both admin accounts.
Is there any other possibility to delete the initial admin account? I did not find any delailed instructions on that issue in the web

Thanks in advance … Max